Since the structure of carbon nanotubes (CNTs) was found in 1991 for the first time, intensive studies about the synthesis, physical properties and application of CNTs have been conducted. In addition, it was found that CNTs are produced upon the addition of a transition metal, such as Fe, Ni or Co, during electric discharge. Since a substantial amount of samples was made by laser evaporation in 1996, studies of CNTs have been raging. Such CNTs have a hollow tube-like shape wound spherically at a graphite surface with a nano-scaled diameter. Herein, depending on the angle and structure of such winding of the graphite surface, CNTs are characterized electrically as conductors or semiconductors. Further, CNTs are classified, depending on the number of graphite walls, into single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), thin multi-walled carbon nanotubes, multi-walled carbon nanotubes (MWCNTs) and roped carbon nanotubes.
In particular, CNTs have excellent mechanical strength and elasticity, are chemically stable and eco-friendly, and show electrically conductive or semiconductive properties. In addition, CNTs have a diameter of 1 nm to several tens nanometers and a length of several micrometers to several tens micrometers. Therefore, CNTs have an aspect ratio of about 1,000 and thus are larger than any known materials. Further, CNTs have a very large specific surface area, and thus have been spotlighted as an advanced material leading the 21st century in the fields of next-generation information electronical materials, high-efficiency energy materials, highly functional composite materials and eco-friendly materials.
Such CNTs are used currently as conductive and reinforcing materials not only in polymers but also in other matrix materials, such as ceramic, metal, etc. Under these circumstances, active studies of CNTs for use in such applications have been made currently. Particularly, many attempts have been made to obtain highly conductive composite materials as high-added value materials by mixing CNTs with other materials in order to overcome the problems of high cost of original materials (CNTs) used alone and poor dispersibility thereof, when using CNTs as materials for improving certain physical properties, including conductivity, in matrix materials, such as polymers.
Korean Patent No. 706652 discloses an electrically conductive thermoplastic resin composition, including 80-99 parts by weight of a thermoplastic resin; 0.1-10 parts by weight of CNTs; and 0.1-10 parts by weight of organic nanoclay.
In addition, Korean Patent Laid-Open No. 2006-52657 discloses a composition, including: 99.6-10 parts by weight of a thermoplastic resin; 0-50 parts by weight of at least one rubber-elastomer; 0.2-10.0 parts by weight of carbon nanofibrils; 0.2-10.0 parts by weight of at least one microparticulate carbon compound, preferably carbon black or graphite powder; and 0-50 parts by weight of at least one filler and/or reinforcing agent.
However, the above compositions still have problems in that CNTs are not dispersed well in a matrix so that they realize maximized functions, and the intermiscibility of the resultant composite materials is too low to form electroconductive flow. Thus, to obtain a desired degree of conductivity, an undesirably large amount of CNTs and composite materials is used, resulting in degradation of the physical properties of the matrix.